My criticism of TeaTime is straightforward. You've planned a hundred steps ahead of where you are. Where are the people? Focus on building TheAudience (aka the market), rather than building the technology.
Upon reflection, my feeling is that I don't need anything special -- the only change I would really make right now is to start using a RSS aggregator so that I don't have to choose between checking all of my micro-wikis daily or settling infrequent updates.
Another TeaTime-like project: http://friendfeed.com/dango-project. It has the advantage of actually being implemented in beta form, and it seems like it's well on the way to making a federated social network a reality.
Sunir, the reason I planned so much with TeaTime is that I needed confidence that the communities I enjoy the most will be able to scale as needed without destroying their character. I guess it boils down to "don't start something you won't want to finish".